Desvenlafaxine succinate, its chemical name is (1-[2-(dimethylamino)-1-(4-phenol)ethyl]-cyclohexanol succinate, has the following structural formula:

Desvenlafaxine succinate, also called as O-desmethyl venlafaxine succinate, is a succinate salt of O-desmethyl venlafaxine, which is a major metabolite of venlafaxine, and has been shown to inhibit norepinephrine and serotonin uptake. Synthesis of desvenlafaxine and its various salts have been disclosed in several publications (U.S. Pat. No. 4,535,186, WO 00/76955, U.S. Pat. Nos. 6,197,828, 6,689,912, 6,673,838 and 7,026,508).
U.S. Pat. No. 6,673,838 discloses four crystalline polymorphic forms (Form I, Form II, Form III and Form IV) and amorphous form of desvenlafaxine succinate.
New crystalline polymorph of a drug substance may display different melting point, hygroscopicity, stability, solubility and/or dissolution rate, crystallinity, crystal habits, bioavailability and formulation handling characteristics, which are among the numerous properties that need to be considered in preparing medicament that can be effectively administered. Therefore, the regulatory agencies require a definitive control of polymorphic form of the active component in solid pharmaceutical dosage forms.
Accordingly, there is an ongoing need to search new polymorphic forms of desvenlafaxine succinate that have better thermal stability and material flow character, lower water contents, and offer advantages for preparing reproducible pharmaceutical formulations. The novel and new polymorphic forms of desvenlafaxine succinate in the present invention help fulfill this and other needs.